In the following analysis, we compare the total owning costs of two backup power options. The total owning cost is comprised of two ﬁgures: the initial purchase price of each piece of equipment and the yearly running cost of each piece of equipment.
Option A depicts a system that has, for the past quarter century, been applied to mitigate power anomalies. Option A relies upon a UPS to provide sag and surge protection and to supply full power to sensitive and critical loads (~15%) during brownouts. It also relies upon diesel generation to power essential services, such as HVAC, refrigeration and elevators.
Option B supplements Option A with an EVR, which allows the system to remain at full power without diesel backup during power surges, sags and brownouts of any duration. The addition of the EVR not only reduces reliance on diesel, but it also reduces wear and tear on the UPS. Because the EVR will compensate for all surges, sags and brownouts, the UPS will have fewer on/oﬀ cycles and less required maintenance.
Option A: 1200 KVA System as designed, with a 200 KVA UPS system deployed to protect critical and sensitive loads, such as sensitive computing equipment, and a 1200 KVA diesel generator to power essential services. In this option, the generator control is set to initiate when the local voltage drops below 90%.
Yearly Running Cost:
The cost of a diesel generator running at ¾ load is approximately $630/hour. This ﬁgure assumes that diesel fuel costs a conservative $10/gallon delivered and .07 G/KWH. The annual cost for UPS maintenance, battery replacement and cost of losses is estimated at $21,300 per year.
|YRS||100 HOURS||200 HOURS||300 HOURS||400 HOURS|
|0||407.0 K$||407.0 K$||407.0 K$||407.0 K$|
|1||554.3K$||617.3 K$||680.3 K$||743.3 K$|
|2||701.6K$||827.6 K$||953.6K$||1079.6 K$|
|3||848.9 K$||1037.9 K$||1226.9 K$||1415.9 K$|
|4||996.2 K$||1248.2 K$||1500.2 K$||1752.2 K$|
|5||1143.5 K$||1458.2 K$||1773.0 K$||2088.5 K$|
Option B: 1200 KVA System as designed in Option A, to provide power to critical and essential services. In Option B, however, an EVR has been installed between the utility system and the load to reduce reliance on diesel generation during brownouts and to mitigate the sags and surges that would otherwise trigger the backup system. When Option B is utilized, the generator will not need to run until the system voltage reaches 75%—considerably less than in Option A. Were we to go further and factor in residual losses caused by power-related business disruptions, ownership costs would be further reduced.
Yearly Running Cost:
Once again, the cost of a diesel generator running at ¾ load is estimated at $630/hour. This ﬁgure assumes that diesel fuel costs a conservative $10/gallon and .07 G/KWH). The annual cost for UPS maintenance, battery replacement and cost of losses is estimated at $21,300 per year.